1. Field of the Invention
This invention relates to a rotating actuator for use with valves and chokes that features a driving member with a variable helix angle. This variable helix angle allows the actuator to generate greater torque near the end of its travel when it is needed to close a valve or operate a choke. The high torque rotating actuator lends itself to use with a subsea drilling and production system used in offshore oil and gas wells. This system uses an extension spool between the standard wellhead and production flow package. Flow control valves are positioned in the extension spool. These valves are ball type valves requiring a 90 degree rotation of the valve between the open and closed positions. Since these valves are being used subsea at water depths beyond the access of divers, remote actuation of the valves is required. The high torque rotating actuator of the present invention allows remote operation of the valve and provides additional torque required to operate the valve when it is needed most.
2. Description of the Related Art
U.S. Pat. No. 4,925,154 to G. S. Baker shows a gate valve with a supplemental actuator. The supplemental actuator uses a series of roller cams with the actuator spring to increase the closing force of the actuator during the last portion of its stroke.
A helically shaped cam for operating a gate valve is shown in the brochure entitled "The Cameron 1/2 10,000 psi WP Half-Turn Manual Gate Valve". The assignee of the current invention manufactures and sells this valve.